Increase in L cell number in ileum. A and B, Photomicrographs illustrate cells immunostained for GLP-1 in ileum of *Gcgr*^{+/+} (A) and *Gcgr*^{−/−} (B) mice. *Scale bar*, 20 μm. C, Histogram documents that the number of L cells per villus and crypt is higher in *Gcgr*^{−/−} than in *Gcgr*^{+/+} mice; n = 6 mice per line, at least 300 villi, and crypts per mouse were scored. **, *P* < 0.005. D, Immunohistochemical localization of GLP-1 (*red*) and GIP (*green*) in a LK cell (*yellow*) located in the ileum of *Gcgr*^{−/−} mice. *Scale bar*, 15 μm. E, The number of cells coexpressing GLP-1 and GIP (LK cells) per villus plus crypt of ileum is higher in *Gcgr*^{−/−} than in *Gcgr*^{+/+} mice; n = 4 mice per line. *, *P* < 0.05. F and G, Representative sections document that the thickness of the intestinal wall and villi length were similar in *Gcgr*^{+/+} (F) and *Gcgr*^{−/−} (G) mice. H, Villi in ileum of *Gcgr*^{+/+} and *Gcgr*^{−/−} have similar surface area; n = 4 mice per line, and at least 100 villi were scored per animal. I, Graph illustrates the specific increase in the ratio of LK cells over total number of L cells scored in ileum of *Gcgr*^{−/−} and *Gcgr*^{+/+} mice. *, *P* < 0.05; n = 4 per line. J, Duodenum of *Gcgr*^{−/−} and *Gcgr*^{+/+} mice have similar number of cells coexpressing GLP-1 and GIP (LK cells); n = 4 mice per line. K, Photomicrograph illustrates two GLP-1^{+} (cytoplasm, *red*) and Pdx-1^{+} (nucleus, *green*) cells in the ileum of *Gcgr*^{−/−} mice. *Scale bar*, 15 μm. For all measurement of cell numbers, at least 300 villi plus crypt were scored.

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